Louvre / Guardrail 1

[KootK]

So I've got a louvre that occupies one entire exterior wall bay of a a pedestrian bridge. I've been asked to evaluate said louver for environmental loads AND guardrail loads. Very glamorous. I'm seeking guidance with respect to the following:

1) Are there any standards out there for louver design? Guidance with regard to treatment of wind and ice loads on a partially open element?

2) Does it make sense to assume that the one horizontal louver at around 42" IS the guardrail for all intents and purposes? Seems kind of extreme. Could one at least say that a few louvers near to 42" share the load?

3) Following the code to the letter, one would have to apply the guardrail load in any direction. That could be problematic here as that would mean applying the load at 45 degrees, weak axis to the louver z-shapes which surely suck for that.

4) Is it even appropriate to be considering a louver as a guardrail? Fundamentally, I feel that a louver is really a permutation of a wall. I might be throwing myself under the "bad engineer" bus here but it's not as though I've been checking my above grade exterior walls for guard rail loads. Although I do do that for glass in some instances...

I'd be grateful for help with any or all of points one through four above. Guardrail struggles seem to be a ubiquitous right of passage on this forum. My tour of duty is probably overdue.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

4) Is it even appropriate to be considering a louver as a guardrail?

I'd ask a Code official that one......but my gut instinct is: no. I had my hand slapped once by such an official because a barrier I provided did not have a graspable hand rail. He agreed no one could fall off/under the thing.....but that had to be there in my situation. Not sure if this falls under the same requirements though.

 

[dhengr]

KootK:
Just food for thought and reinforcement for an argument, no profound profundities.
Is this a bridge or walkway for the general public use, or is primarily an in-plant access/egress and mechanical access walkway? Then does the IBC or OSHA govern? It doesn’t need a handrail/guardrail, you can’t fall through it or over it, and that is the primary reason for a handrail/guardrail. If anything, you might treat this more like a set of horiz. balusters, and there the design load is some load (50lbs./sq.ft. ?) on a one sq.ft. area on the surface, that would be at least several louvers. This because you can’t climb over it, fall over or through it to a lower level. Do you have to design every vert. wall surface, at 42" ht., for guardrail loads in any possible direction? The bridge structure should be separated from the mech. louver, and as such you should/could put the same guardrail as is on the other side of the bridge. OSHA says the walking surface should be within a couple inches of a vert. surface (wall, tank, etc.) so large items can’t fall through, to below, and then you should have a kick pl. 4-5" above the walking surface. How would you ever apply the 200lb. load at 45̊, except with a 2x4, on end, and very large impacting load (hammer), and with the intent to destroy. That’s not like sitting on the guardrail or some such.

 

[bridgebuster]

KootK,

Regarding 1), there should be something in ASCE-7. A louvre is akin to screening. I'm leaning towards your idea of using the louvre as the guardrail. Here's why: On recently renovated NYC Transit elevated stations, they use a mesh as a barrier. I'll see if I have a detail so that you can make a comparison.

 

[XR250]

I have always treated them as solid elements for wind loads - I figured that was conservative (but maybe not1)
I agree with dhengr and consider it guardrail infill.

Are you out on your own now?

 

[bridgebuster]

KootK - here's the screen detail I mention; not quite what you're dealing with but it's used all over the city on elevated stations.

 

[MotorCity]

For environmental loads, I would be comfortable in assuming that the manufacturer has already designed it for wind load since that is its intended purpose.

What makes it necessary to utilize it as a guardrail, is there guardrail adjacent to the louver? I would not use it as a guardrail without buy off from the code official and the manufacturer (both of whom I think would deny such a request). If one were to check it, I suspect that the fins of the louver are probably a gage material and would most likely fail under guardrail loads (especially given the previous debates on eng-tips about getting certain size pipes to work for guardrail). I would look into putting a guardrail next to the louver if that's possible.

 

[racookpe1978]

Well, a separate 36 inch high handrail is not needed on a 42 inch horizontal guard rail.

The individual sections (complete panels) of the louver are the assembled panels, and they need to withstand the 200 lbs force per "post" horizontal force at the topof the gaurdrail (or 50 lbsf per foot horizontal, usually considered equally distributed on four-foot distances between posts.

Best way is to "test" the assembled panel by pushing on it in the center of the panel, 42 inches up. Now, if the panel is 60 inches high, then you'd need to either assume the total load is at the 60 inch high distance, or be able to prove somehow that the load is actaully being applied only 42 inches up.

The real load is going to be distributed between the frame on top of the panel, the first, second, third and fourth sections. Most load on top, then probably about 20, 15, 10%, 5% as you go down.

 

[CANPRO]

Kootk, from previous posts (you have a few) I know you're in Canada. I believe the NBCC addresses the condition of a wall acting as a means of fall protection. As you noted in your point #4, your condition is more like a wall than a guardrail. I don't have the building code in front of me, but I'm fairly certain there is specific mention of a wall separating a change of elevation greater than 600mm.

 

[CANPRO]

kootk, NBCC 2010 cl. 4.1.5.16. specifically covers walls acting as guards. Specified lateral load of 0.5 kPa

 

[racookpe1978]

You "may" face an extra snow load here: Big snow, snow is trapped between the two ?? louvers and the walkway, rather than falling through or not being trapped at all as if it were between two open handrails and posts. Will that trapped snow/ice/meltwater (24 inch ??) be a significant (even if scarce) load?

Wind loads significant? Sideways force will be across a "near-solid panel" rather than an open walkway and open handrails with near-zero wind resistance.

Toeboard/kickplate needed? Kickplate not needed but wanted to keep damage from occurring to the louver at the bottom?

 

[KootK]

Thanks all.

Are you out on your own now?

Why ever would you say that? For all you know, I'm designing my sad little louver from my VP corner office at Thornton Tomasseti.

Yeah, totally out on my own now. Hungry like the wolf.

Big snow, snow is trapped between the two ?? Will that trapped snow/ice/meltwater (24 inch ??) be a significant (even if scarce) load?

Perhaps in general but not in this instance. Despite my Canuck-ed-ness, this bad boy's actually going up in Missouri.

Is this a bridge or walkway for the general public use, or is primarily an in-plant access/egress and mechanical access walkway?

Mechanical access walkway & OSHA. We've decided to follow your approach and address it using the infill provisions.

Do you have to design every vert. wall surface, at 42" ht., for guardrail loads in any possible direction?

Honestly, I'm unsure now. I haven't been doing that for opaque walls but it's actually quite common to do it for glazing for some reason. Canpro's shed some light on this, at least north of the border.

Toeboard/kickplate needed? Kickplate not needed but wanted to keep damage from occurring to the louver at the bottom?

Fair points. I'll check with OSHA and the owner.

For environmental loads, I would be comfortable in assuming that the manufacturer has already designed it for wind load since that is its intended purpose.

Alas, I kind of am the manufacturer here. Happy to take advice on "pop rivets" as well, whatever the heck those are.

What makes it necessary to utilize it as a guardrail, is there guardrail adjacent to the louver?

What makes it necessary is, essentially, just my client's wishes and my newfound uncertainty regarding whether or not such treatment is necessary. No guardrail adjacent to the louver.

If one were to check it, I suspect that the fins of the louver are probably a gage material and would most likely fail under guardrail loads (especially given the previous debates on eng-tips about getting certain size pipes to work for guardrail)

Accurate. No chance for anything other than the infill load requirement.

I would look into putting a guardrail next to the louver if that's possible.

That's starting to make a lot of sense. Given my role in the project, however, I suspect that we're a little too far down the path for that.

kootk, NBCC 2010 cl. 4.1.5.16. specifically covers walls acting as guards. Specified lateral load of 0.5 kPa

Thanks for that. The clip below is taken from APEGBC's guard doc. I've been taking that to mean guard rail loads. Perhapss it really means the walls as guard loads. That would be less punitive and, certainly, a lot friendlier computationally. It also leads me to wonder just what qualifies as a "wall". For example, this morning, I was looking at a 8' high glass enclosure around a patio with a elevation drop outside the patio. The glass spanned horizontally between cantilevered wood posts. Wall as guard? Or guard rail? Is a wall to simply be thought of as something without a physical rail? Or as something with lateral support at the top?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.